A. Adrenergic Receptors Phenothiazines are a class of drugs used in psychiatric

Question

A. Adrenergic Receptors Phenothiazines are a class of drugs used in psychiatric medicine. These drugs are alpha 1 blocking agents. Their effects on the CNS are useful to treat various psychoses. However they also have peripheral side effects, including changes in pupil diameter and blood pressure. Remembering that constricting blood vessels tends to increase blood pressure and dilating blood vessels tends to reduce blood pressure, explain these side effects by answering the following questions: 13. a) What effect does epinephrine/norepinephrine have on the alpha receptors of the iris of t eye or the skeletal muscle vasculature? b) What would be the result in each of those places if the alpha 1 receptors were blocked? That explains why you can often tell which types of medication people are taking by looking at their pupils! c) Many illegal drugs are sympathetic agonists. What would the pupils of someone taking such sympathomimetic drugs look like?

Explanation / Answer

Hi,

The hormones epinephrine and norepinephrin are secreted by adrenaline glands. These binds to alpha and beta receptors of various muscles including iris of eye and skeletal muscles. The binding of these hormones to iris of the eye can cause constriction of the iris. In the skeletal muscle it causes the vasodilation and constriction.

Blocking of alpha 1 receptor can inhibit the action of these hormones resulting in dilation of pupil and also the skeletal muscle fails to constrict. Eyes don't respond to light or other stimuli. That's why they always looks large and dilated.

Drugs often block the receptors of these two hormones. So the person under such medication would experience dilated pupil, increased heart rate and blood pressure, restlessness and lack of sleep.

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